I'm in the middle of replacing a shower handle, switching from three handles to a single handle setup. While I was at it, I discovered some mold on the cement board and ended up needing to rip apart a few tiles. Now I need to figure out the best way to close up the seam between the old cement board and what's left behind. I'm looking for advice specifically on how to patch the edges on both sides without having to take down more tiles than necessary. Here's a link to some pictures for reference: [imgur](https://imgur.com/a/0QMBFfM).
2 Answers
Just a heads up, it looks like you’ve got drywall there instead of cement board. You can use mesh tape and thinset for the seams you can reach, and for the spots you can’t, urethane caulk works well. I'd also recommend applying a liquid waterproofer like Aquadefense before you tile back up, just to be safe!
Are you sure that’s cement board? It looks like drywall because of the paper on the surface. Based on what I can see in the pics, it might be drywall since there’s tile failure in the corner. If it is cement board, you’d want to use alkali resistant fiberglass tape with thinset to seal it up. Remember, patching can be tricky when it comes to waterproofing, and it doesn’t seem like you have a proper waterproof system in place.
Thanks for the tip! Yup, what I have left is indeed drywall. I’ll patch it up with cement board and make sure to waterproof it well. I’ll also use mold-resistant paint where it’s visible before tiling again.
Got it! So the exposed part is drywall. I checked and the piece I removed was definitely cement board. I think I’ll do what you suggested and patch up with cement board, then waterproof it to prevent any issues.